LOTS of benefits to this. And required for most tech diving certifications.
Other benefits include:
A panicked diver will go for your Primary regulator anyway, so you give it to them, and switch to your secondary which sits near your mouth.
This also reduces the chance they put it in their mouth upside down.
Drawbacks:
Not typically available for rentals.
Added bulk for travel.
Not ideal for rapid deployment rigs, shooting action video in and out quickly (not a major drawback but definitely adds a tad more drag & process).
